Mobile terminals, such as a mobile phone, a personal digital assistant (PDA), and the like, are driven with rechargeable batteries due to their nature, and the battery of the mobile terminal is charged through supplied electronic energy by using a separate charging apparatus. Typically, the charging device and the battery have separate contact terminals at an exterior thereof, respectively, and are electrically connected with each other by contacting the contact terminals.
However, in such a contact-type charging scheme, the contact terminals protrude outwardly, and thus are easily contaminated by rogue objects. As a result, battery charging is not correctly performed. Further, the battery charging may also not be correctly performed in a case where the contact terminal is exposed to moisture.
Currently, a wireless charging or a non-contact charging technology is developed and used for electronic devices to address the above-mentioned issue.
The wireless charging technology uses wireless power transmission and reception, and corresponds to, for example, a system in which a battery is automatically charged if the battery is just put on a charging pad without connecting the mobile phone to a separate charging connector. Generally, a wireless vibration tooth brush or a wireless electric shaver is known to an ordinary person. The wireless charging technology can improve a waterproof function because the wireless charging technology can be used to wirelessly charge the electronic devices. The wireless charging technology can improve the portability of the electronic devices because the wireless charging technology does not require a wired charger. Therefore, it is expected that technologies related to the wireless charging technology will be significantly developed in the coming age of electric cars.
The wireless charging technology largely includes an electromagnetic induction scheme using a coil, a resonance scheme using a resonance, and a radio frequency (RF)/microwave radiation scheme converting electrical energy to a microwave and then transmitting the microwave.
It is considered up to now that the electromagnetic induction scheme is mainstream, but it is expected that the day will come when all electronic products are wirelessly charged, anytime and anywhere, without a wire in the near future on the strength of recent successful experiments for wirelessly transmitting power to a destination spaced away by dozens of meters through the use of microwaves at home and abroad.
A power transmission method through the electromagnetic induction corresponds to a scheme of transmitting electric power between a first coil and a second coil. When a magnetic is moved in a coil, induction current occurs. By using the induction current, a magnetic field is generated at a transferring end, and electric current is induced according to a change of the magnetic field so as to make energy at a reception end. The phenomenon is referred to as the magnetic induction, and the electric power transmission method using magnetic induction has high energy transmission efficiency.
With respect to the resonance scheme, Prof. Soljacic of the Massachusetts Institute of Technology (MIT) announced a system in which electricity is wirelessly transferred using an electric power transmission principle of the resonance scheme based on a coupled mode theory even if a device to be charged is separated from a charging device by several meters. A wireless charging system of an MIT team employs a concept in physics that resonance is the tendency in which when a tuning fork is at a particular frequency, a wine glass next to the tuning fork oscillates at the same frequency. The research team makes an electromagnetic wave containing electrical energy resonate instead of making sounds resonate. It is known that the resonant electrical energy does not affect surrounding machines and human bodies differently from other electromagnetic waves because the resonant electrical energy is directly transferred only to a device having a resonance frequency and the unused part of the resonant electrical energy is reabsorbed into an electromagnetic field instead of spreading into the air.
Meanwhile, active researches on a wireless charging method are currently being progressed, but standards for a wireless charging order, a search for a wireless power transmitter/receiver, selection of a communication frequency between the wireless power transmitter/receiver, a wireless power control, selection of a matching circuit, communication time distribution to each wireless power receiver in one charging cycle have not been proposed. More particularly, it is required to propose a standard for a configuration and a procedure in which the wireless power receiver selects the wireless power transmitter to receive wireless power.
The wireless power transmitter and the wireless power receiver may communicate based on a certain scheme, for example, a Zig-bee scheme or a Bluetooth low energy scheme. By using an out-band scheme, such as the Zig-bee scheme or the Bluetooth low energy scheme, the available distance of communication increases. Thus, the wireless power transmitter and the wireless power receiver may perform communication even though the wireless power transmitter and the wireless power receiver are located at a relatively far distance. For example, the wireless power transmitter may perform communication with the wireless power receiver even though the wireless power transmitter is located at a relatively far distance where wireless power cannot be transmitted.
In a wireless power transmitter using the existing differential signal, there are problems in which the amplitudes and phase differences of two signals in the differential signal do not correspond according to positions of the resonance unit of the wireless power transmitter and the resonance unit of the wireless power receiver. Thus, there are problems in which it is difficult for the wireless power transmitter to maintain a wireless power transmission efficiency and the harmonic wave restrain nature is deteriorated.
Therefore, a need exists for a wireless power transmitter capable of controlling an amplitude and a phase difference of a differential signal and a method of controlling the wireless power transmitter.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.